The present invention relates to a process for consolidating geological formations, this process being in particular applicable to oil and gas reservoirs, to prevent sand from flowing into a well traversing unconsolidated, or insufficiently consolidated, sand formations.
More generally this process can be used to locally consolidate permeable formations.
Various methods have been proposed to prevent sand from flowing into new boreholes, or to treat wells liable to be subjected to sand flowing during exploitation of oil or gas deposits.
A first type of method consists of maintaining the sand by mechanical means, using artificial screens with calibrated apertures, or packs of gravels having a well-defined size distribution, depending on the size of the sand particles or grains of the geological formation traversed by the borehole. Such a method is very often applied to new wells, but is difficult to put into operation.
A second type of method consists of injecting into the geological formation a liquid resin which by polymerization creates a bond between the sand grains.
The efficiency of a chemical method of this second type is uncertain, since the reaction of polymerization of the injected resin depends essentially on the conditions prevailing in the borehole at the level of the formation and on the characteristics of the latter. Thus, such a method does not permit control of the extent of the chemical reaction.
There is thus the risk either of an insufficient consolidation of the formation if the degree of polymerisation of the resin is not sufficient, or of an excessive reduction of the permeability of the geological formation, or even of complete plugging thereof, if a too great an amount of polymer is retained in some of the pores of the formation.
Another method, which is described in British Pat. No. 975,229, consists of successively introducing into the formation a material consisting essentially of an unsaturated fatty acid, then an oxygenated gas, with a view toward obtaining a resinification of said material.
However a proper consolidation is obtained by this method only if the formation to be consolidated is at a temperature comprising between 150.degree. and 300.degree. C., or is heated to such a temperature which is much higher than the normal temperature of oil or gas reservoirs.
It has also been contemplated in this prior patent to add a catalyst made of cobalt naphthenate, or manganese naphthenate.
Even in this last case the so obtained consolidation is really satisfactory only if the temperature of the formations is sufficiently high.
U.S. Pat. No. 3,388,743 also discloses a consolidation method wherein injection of a drying oil into formations surrounding a borehole is followed by the injection of an oxidizing gas.
The partially oxidized oil constitutes a good binding material for the sand particles.
By using an oxidizing catalyst, such as lead or cobalt naphthenate it is possible to shorten the time required for oxidizing the oil.
However, the consolidation obtained by application of this method is generally insufficient for the object at which it is aimed.
From French Pat. No. 1,409,599 also teaches a process for consolidating the grounds wherein these grounds are treated by oily polymers containing siccative or drying catalysts which are hardened by air drying on the surface of the ground to be consolidated.
This treatment which produces hard, impermeable ground masses is however not suitable for consolidating subterranean formations whose permeability must be preserved.